1. Field of the Invention
The present invention relates to antennas, and particularly to a ferrite-loaded, Fabry-Perot Cavity antenna that achieves a −10 dB impedance bandwidth of 525 MHz, directivity of 11.04 dB, controlled side lobe level and a phase shifter less broadside beam scanning of ±12° for 200 kA/m changes in the externally applied axial magnetizing field.
2. Description of the Related Art
The use of radars in the aviation industry has had a long history. Traditional radar systems radiate a high-power signal at a certain frequency, and point it towards a desired direction. Historically, the radar antenna was mechanically rotated to cover the complete 360° azimuth plane and the reflected signals from the targets illuminated by the radar beam were monitored to locate the targets. As the antenna fabrication and microcontroller technology progressed, electronic beam scanning came into being. In a uniform phased array antenna, the idea of electronic beam scan involves introducing a progressive phase shift in the input excitation of the antenna array elements. Depending on the type of the antenna array, variation of the progressive phase shift causes the main beam to steer/scan along the azimuth or the elevation planes.
Although the idea of progressive phase shift introduced in the array elements works well, implementing phase shifters in the antenna array feed network presents a considerable challenge. Antenna array designs employing microstrip patch elements often require a complete redesign of the existing feed network. Analogue or digital ferrite phase shifters have been widely used in phased array systems to introduce externally tunable progressive phase shift, needed for beam scanning.
Beam shaping/scanning can also be realized by composite ferrite-dielectric partially reflecting superstrate, placed above the radiating elements, to influence the radiated electromagnetic (EM) wave. This phase shifter less beam scanning is particularly important for a Fabry-Perot cavity (FPC) antenna, excited by minimum number of array elements to minimize feed network complexity and losses.
Radiation properties of a microstrip 2×1 array can be considerably improved, by letting it optimally excite a larger Fabry-Perot cavity (FPC) antenna, formed between the ground plane and the partially reflecting superstrate (PRS). Over the years, researchers have used frequency selective surfaces (FSSs), electromagnetic bandgap structures (EBGs) and artificial magnetic conductors (AMCs) to realize PRSs that can improve the gain, directivity and beam-shaping performance of a microstrip array antenna.
But optimal excitation of FPCs using a 2×1 microstrip array often requires a large spacing (d>λ/2) between the array elements (thinned array). This introduces grating lobes during the beam scanning process of the antenna.
Thus, a ferrite-loaded, Fabry-Perot Cavity antenna with composite superstrate is proposed to solve the aforementioned problems.